This invention relates to an apparatus and such containers for the processing of liquid-containing substance mixtures, particularly fiber pulp suspensions of cellulose pulp, which are designed for axial flow of the fiber pulp suspension and comprise at least one set of screen bodies disposed substantially on the same level for screening-off liquid which is not desired in subsequent treatment steps. This treatment of the fiber pulp suspension can be carried out by concentration, washing, chemical treatment, particularly bleaching, or similar treatments with the object of removing at least part of the liquid, in which the fiber pulp is suspended.
When there is a pulp concentration of 2-4% to 8-15%, the liquid amount to be removed is drained through the screen bodies without supply of compensating liquid. When washing or bleaching, particularly when so-called dynamic bleaching, treatment liquid is supplied through special means. The treatment liquid may be water or washing liquid or liquid of a chemical strength lower than that of the suspension liquid to be exchanged and, respectively, bleaching liquid, extraction liquid such as alkali or water. The supply means are located in connection to the screen bodies in such a way that the agent supplied is passed through the fiber pulp suspension transversely in relation to the flow direction of the suspension. As a result of this transverse flow, the liquid, in which the cellulose-containing material is suspended, is replaced entirely or partially by the liquid supplied.
Known designs of the aforesaid apparatus are provided with a plurality of cylindric screen bodies, which have different diameters and are arranged concentrically for screening across the entire cross-section of the container. Treatment liquid is spread between the screen bodies from spray pipes rotating in concentric paths to spread the liquid in two opposed radial directions. One difficulty in this conjunction is to distribute the liquid in correct proportions in one and the other direction, because the liquid most readily flows radially outward to the larger screen surface on the outer screen body. Attempts have been made to counteract this inconvenience by a number of measures which, however, did not bring about a fully satisfactory result. The problems with concentric cylindric screen bodies is mirrored by the discussion covered in the Swedish patent specifications 225 814, 341 654, and 342 270. A further inconvenience in conjunction with cylindric screen bodies is the difficulty of access to the screen bodies for inspection, cleaning and exchange.